Quantum dot, manufacturing method of the dot, and compact, sheet member, wavelength conversion member and light emitting apparatus using the quantum dot

ABSTRACT

To provide a quantum dot and manufacturing method of the dot particularly capable of reducing organic residues adhering to the quantum dot surface and of suppressing the black discoloration occurrence of a layer including the quantum dot positioned immediately above a light emitting device, and a compact, sheet member, wavelength conversion member and light emitting apparatus with high luminous efficiency using the quantum dot, a quantum dot of the present invention has a core portion including a semiconductor particle, and a shell portion with which the surface of the core portion is coated, and is characterized in that a weight reduction up to 490° C. is within 75% in a TG-DTA profile. Further, the quantum dot of the invention is characterized in that oleylamine (OLA) is not observed in GC-MS qualitative analysis at 350° C.

TECHNICAL FIELD

The present invention relates to a quantum dot, manufacturing method ofthe dot, and a compact, sheet member, wavelength conversion member andlight emitting apparatus using the quantum dot.

BACKGROUND ART

A quantum dot is a nanoparticle having a particle diameter of aboutseveral nanometers to several tens of nanometers comprised of aboutseveral hundred to thousand semiconductor atoms, and forms a quantumwell structure. The quantum dot is also called the nanocrystal.

For the quantum dot, it is possible to modify a peak emission wavelengthin various manners, corresponding to the particle diameter andcomposition of the crystal. For example, as in Patent Documents 1 and 2,a light emitting apparatus is known where a fluorescent layer includingquantum dots is arranged around an LED chip.

PRIOR ART DOCUMENT Patent Document

[Patent Document 1]

Japanese Unexamined Patent Publication No. 2008-130279

[Patent Document 2]

Japanese Unexamined Patent Publication No. 2012-204609

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, in conventional light emitting apparatuses, it has been foundthat black discoloration occurs in the fluorescent layer includingquantum dots positioned immediately above the LED chip by emission ofthe LED chip, and that luminous efficiency of the light emittingapparatus deteriorates. Then, the applicant found out that a cause ofblack discoloration of the fluorescent layer is an effect of organicresidues deriving from quantum dot raw materials adhering (adsorbed) tothe quantum dot surface.

The present invention was made in view of such a respect, and it is anobject of the invention to provide a quantum dot and manufacturingmethod of the dot particularly capable of reducing organic residuesadhering to a quantum dot surface and of suppressing the blackdiscoloration occurrence of a layer including the quantum dot positionedimmediately above a light emitting device, and a compact, sheet member,wavelength conversion member and light emitting apparatus with highluminous efficiency using the quantum dot.

Means for Solving the Problem

A quantum dot in the present invention is characterized in that a weightreduction up to 490° C. is within 75% in a TG-DTA profile.

Further, a quantum dot in the invention is characterized in thatoleylamine (OLA) is not observed in GC-MS qualitative analysis at 350°C. At this point, it is preferable that trioctylphosphine (TOP) is notobserved in GC-MS qualitative analysis at 350° C. In addition, it ispreferable that a weight reduction up to 490° C. is within 75% in aTG-DTA profile.

Further, a quantum dot in the invention is characterized by beingcleaned with an ultracentrifuge.

Furthermore, the quantum dot in the invention may be comprised by havinga core portion including a semiconductor particle and a shell portionwith which the surface of the core portion is coated.

Still furthermore, in the invention, the shell portion is capable ofbeing made a configuration having a first shell portion with which thecore portion is coated, and a second shell portion with which thesurface of the first shell portion is coated.

Moreover, a compact in the invention is characterized by being made byhaving the quantum dot as described in one of above-mentioned items.Further, a sheet member in the invention is characterized by being madeby having the quantum dot as described in one of above-mentioned items.Furthermore, a wavelength conversion member in the invention ischaracterized by having a container provided with storage space, and awavelength conversion layer including the quantum dot as described inone of above-mentioned items disposed inside the storage space to becomprised thereof.

Further, the invention provides a light emitting apparatus having afluorescent layer covering a light emitting side of a light emittingdevice, and is characterized in that the fluorescent layer is formed ofa resin with the quantum dot as described in one of above-mentioneditems dispersed.

Furthermore, the invention provides a light emitting apparatus having afluorescent layer covering a light emitting side of a light emittingdevice, and is characterized in that the fluorescent layer is formed ofa resin with the quantum dot dispersed, and that black discoloration byemission of the light emitting device does not occur in the resin layer.

Still furthermore, the invention provides a method of manufacturing aquantum dot having a core portion including a semiconductor particle,and is characterized in that a quantum dot solution is prepared byhaving a step of synthesizing the semiconductor particle to form thecore portion, and that an ultracentrifuge is used in a step of cleaningthe quantum dot solution.

In the invention, the method includes a step of coating the surface ofthe core portion with the shell portion after the step of forming thecore portion, and it is possible to shift to the cleaning step aftercoating with the shell portion.

Further, in the invention, the shell portion is capable of being formedby having a first shell portion with which the core portion is coated,and a second shell portion with which the surface of the first shellportion is coated.

Advantageous Effect of the Invention

According to the present invention, it is possible to provide thequantum dot with little adhesion of the organic residue on its surface,and it is possible to manufacture such a quantum dot with easeefficiently.

Further, it is possible to effectively suppress the black discolorationoccurrence of the layer including the quantum dot positioned immediatelyabove the light emitting device.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are schematic diagrams of an LED apparatus (lightemitting apparatus);

FIG. 2 is a schematic diagram of a quantum dot;

FIG. 3 is a schematic diagram of another LED apparatus (light emittingapparatus);

FIG. 4 is a schematic diagram of a resin compact provided with quantumdots;

FIG. 5 is a perspective diagram of a resin formed sheet provided withquantum dots;

FIG. 6A is a longitudinal sectional diagram of a sheet member providedwith quantum dots and FIGS. 6B and 6C are schematic diagrams ofapplication using the sheet member;

FIG. 7A is a perspective diagram of a wavelength conversion memberprovided with quantum dots and FIG. 7B is a cross-sectional diagramalong arrows A-A;

FIG. 8 is a perspective diagram of a light emitting device comprised byhaving a wavelength conversion member provided with quantum dots;

FIG. 9 is a longitudinal sectional diagram taken along line B-B in theheight direction viewed from the arrow direction in a state in whicheach component of the light emitting device shown in FIG. 8 is combined;

FIG. 10 is a flowchart illustrating a method of manufacturing a quantumdot;

FIG. 11 is a schematic diagram illustrating a first method of cleaningthe quantum dot;

FIG. 12 is a schematic diagram illustrating a second method of cleaningthe quantum dot;

FIG. 13 is a TG-DTA profile of a quantum dot in the Example;

FIG. 14 is a TG-DTA profile of a quantum dot in Comparative Example 1;

FIG. 15 is a TG-DTA profile of a quantum dot in Comparative Example 2;

FIG. 16 is a GC-MS spectrum (350° C.) of the quantum dot in the Example;and

FIG. 17 is a GC-MS spectrum (350° C.) of the quantum dot in comparativeExample 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will specifically be describedbelow. As shown in FIG. 1A, an LED apparatus (light emitting apparatus)1 has a storage case 2 having a bottom 2 a and side walls 2 bsurrounding the circumference of the bottom 2 a, an LED chip 3 disposedon the bottom 2 a of the storage case 2, and a fluorescent layer 4filled inside the storage case 2 to seal the upper surface side of theLED chip 3. Herein, the upper surface side is a direction in which lightemitted from the LED chip 3 is released from the storage case 2, andindicates a direction opposite to the bottom 2 a with respect to the LEDchip 3. Further, in this Embodiment, the LED chip 3 is included incomponents of the light emitting apparatus. Alternatively, the LED chip3 maybe provided separately from the light emitting apparatus. Forexample, it is possible to make a configuration where the LED chip 3 isdisposed outside the light emitting apparatus.

The LED chip 3 is disposed on a base wiring board not shown, and thebase wiring board may constitute a bottom portion of the storage case 2.As the base board, for example, it is possible to present aconfiguration where a wiring pattern is formed on a substrate of glassepoxy resin or the like.

The LED chip 3 is a semiconductor device that emits light in applyingthe voltage in the forward direction, and is provided with a basicconfiguration where a P-type semiconductor layer and N-typesemiconductor layer are subjected to PN junction. Alternatively, as asubstitute for the LED chip 3, it is also possible to use asemiconductor laser and light emitting device such as an EL(Electro•Luminescence) device.

As shown in FIG. 1A, the fluorescent layer 4 is formed of a resin 6 withmany quantum dots 5 dispersed.

Further, a resin compact in this Embodiment may include the quantum dot5 and another fluorescent substance as a fluorescent pigment,fluorescent dye or the like different from the quantum dot 5. Forexample, there are quantum dots of red light emission and fluorescentsubstance of green light emission, or quantum dots of green lightemission and fluorescent substance of red light emission. Among thefluorescent substances are a YAG (yttrium•aluminum•garnet) series, TAG(terbium•aluminum•garnet) series, sialon series, BOS(barium•orthosilicate) series and the like, but materials are notlimited particularly. It is possible to apply such forms to forms otherthan the form of FIG. 1A or 1B as appropriate.

The resin 6 constituting the fluorescent layer 4 is not limitedparticularly, and it is possible to use polypropylene, polyethylene,polystyrene, AS resin, ABS resin, methacrylate resin, polyvinylchloride, polyacetal, polyamide, polycarbonate, modified-polyphenyleneether, polybutylene terephthalate, polyethylene terrain terephthalate,polysulfone, polyether sulfone, polyphenylene sulfide, polyamide imide,polymethyl pentene, liquid crystal polymer, epoxy resin, phenol resin,urea resin, melamine resin, epoxy resin, diallyl phthalate resin,unsaturated polyester resin, polyimide, polyurethane, silicone resin,mixtures thereof and the like.

As shown in FIG. 2, the quantum dot 5 in the present invention has acore portion 7 including a semiconductor particle, and a shell portion 8with which the circumference of the core portion 7 is coated. Forexample, CdSe is used for the core portion 7, but materials are notlimited particularly. For example, it is possible to use a core materialincluding at least Zn and Cd, core material including Zn, Cd, Se and S,ZnCuInS, ZnSe, ZnS, CdS, CdSe, InP, CdTe, mixtures of some thereof, andthe like.

The shell portion 8 protects the core portion 7 as a fluorescentportion. As shown in FIG. 2, the shell portion 8 is comprised oftwo-layer structure, and in other words, is of the so-called multi-shellstructure having a first shell portion (shell I) 9 with which thesurface of the core portion 7 is coated, and a second shell portion(shell II) 10 with which the surface of the first shell portion 9 iscoated. It is suitable that the shell portion 8 thus has two or morelayers, but one layer may be adopted. In such a case, the shell portion8 is comprised of one layer of the second shell portion 10. In addition,in the present invention, it is possible to provide a one-layerstructure controlled so that the composition ratio inside the shellportion gradually changes with distance from the core portion 7, and thelike.

For example, a band gap of the second shell portion 10 is made largerthan a band gap of the first shell portion 9, but the invention is notlimited thereto.

Materials are not limited particularly, and for example, the first shellportion 9 is formed of ZnCdS, while the second shell portion 10 isformed of ZnS.

As shown in FIG. 2, many organic ligands 11 coordinate to the surface(surface of the second shell portion 10) of the quantum dot 5. By thismeans, it is possible to suppress coagulation of quantum dots 5, and itis possible to improve dispersion characteristics of the quantum dots 5inside the resin 6. Materials of the ligands are not limitedparticularly, and examples thereof are octadecene, octadecane,trioctylphosphine (TOP), trialkyl phosphine oxide, alkylamine,dialkylamine, trialkylamine, alkylphosphonic acid and the like.

Alternatively, the quantum dot 5 may be comprised of only the coreportion 7 including the semiconductor particle, without the shellportion 8 being formed. In other words, as long as the quantum dot 5 isprovided with at least the core portion 7, the quantum dot 5 does notneed to be provided with a coating structure by the shell portion. Forexample, when the core portion is coated with the shell portion, thereis a case where the region as the coating structure is small or coatingportion is too thin, and it is not possible to analyze and confirm thecoating structure. Accordingly, irrespective of the presence or absenceof the shell portion by analysis, it is possible to judge as the quantumdot 5.

As shown in FIG. 1B, a resin layer 12 without quantum dots 5 being mixedmay exist between the LED chip 3 and the fluorescent layer 4. The resinused for the resin layer 12 and the resin 6 used for the fluorescentlayer 4 may be made of the same material or different materials. Whenthe resin layer 12 is made different from the resin 6 used for thefluorescent layer 4, for example, a resin with high thermal conductivityis disposed in the resin layer 12, and the resin 6 that enablesdispersion characteristics of the quantum dot 5 to be improved isselected for the fluorescent layer 4. As one example, the resin layer 12is formed of a silicone resin, and the resin 6 used for the fluorescentlayer 4 is formed of an epoxy resin. Further, when the resin layer 12and the resin 6 used for the fluorescent layer 4 is formed of the sameresin, it is possible to use an epoxy resin, silicone resin and the likefor both the resin layer 12 and the fluorescent layer 4.

FIG. 3 is a schematic diagram of another LED apparatus (light emittingapparatus). In an LED apparatus (light emitting apparatus) 38 shown inFIG. 3, the LED chip (light emitting device) 3 is installed on asubstrate 37, and a fluorescent layer 29 is formed over the uppersurface (light emitting surface) of the LED chip 3 and the upper surfaceof the substrate 37. As shown in FIG. 3, the fluorescent layer 29includes the quantum dots 5.

In the LED apparatus (light emitting apparatus) 38 shown in FIG. 3, asdistinct from FIGS. 1A and 1B, without providing the case-shaped storageportion to store the LED chip and fluorescent layer, the fluorescentlayer 29 is formed on the LED chip 3 installed on the substrate 37 bypotting processing and the like.

In FIG. 3, the surface of the fluorescent layer 29 is in the shape of adome. For example, a dent portion may be formed on the surface, theshape maybe rectangular, and thus, the shape is not limitedparticularly.

FIG. 4 is a schematic diagram of a resin compact provided with quantumdots. In FIG. 4, a bar-shaped wavelength conversion member 42 existsbetween light emitting devices 40 such as LEDs and a light guide plate41. In this Embodiment, a resin including quantum dots is formed in theshape of a bar or rod to constitute the wavelength conversion member 42shown in FIG. 4. Light emitted from the light emitting device 40 issubjected to wavelength conversion in the wavelength conversion member42, and the light subjected to wavelength conversion is output to thelight guide plate 41. For example, the wavelength conversion member 42includes each of quantum dots with fluorescent wavelengths of 520 nm(green) and 660 nm (red). Then, a part of blue photons emitted from thelight emitting device 40 is converted into green or red by each ofquantum dots, and white light is thereby output from the wavelengthconversion member 42 to the light guide plate 41.

In FIG. 5, on the light emitting surface of the light guide plate 41 isprovided a wavelength conversion sheet 43 formed by using a resinincluding quantum dots. In this Embodiment, the wavelength conversionsheet 43 may be applied and formed onto the light guide plate 41, or maybe beforehand formed in the shape of a sheet to be stacked on the lightemitting surface of the light guide plate 41. Further, another film suchas a diffusion film may be disposed between the light guide plate 41 andthe wavelength conversion sheet 43.

Further, it is also possible to form the light guide plate 41 itself byusing a resin including quantum dots. In this case, the wavelengthconversion sheet 43 may exist or may not exist. Both the light guideplate 41 and the wavelength conversion sheet 43 are capable of includingquantum dots that emit green light and quantum dots that emit red light.Furthermore, it is also possible that the light guide plate 41 includesquantum dots that emit green light, and that the wavelength conversionsheet 43 includes quantum dots that emit red light. Alternatively,conversely, it is also possible that the light guide plate 41 includesquantum dots that emit red light, and that the wavelength conversionsheet 43 includes quantum dots that emit green light.

FIG. 6A is a longitudinal sectional diagram of a sheet member providedwith quantum dots and FIGS. 6B and 6C are schematic diagrams ofapplication using the sheet member. A sheet member 45 has a quantum dotlayer 46 having quantum dots, and barrier layers 47, 48 formed on theopposite sides of the quantum dot layer 46 to be comprised thereof.Generally, the “sheet” is regarded as a configuration where itsthickness is thin with respect to the length and width. The presence orabsence of flexibility of the sheet member 45 is not required, but it issuitable that the sheet has flexibility. The sheet member 45 maysometimes be called simply a sheet, or may be called a film, film sheetor the like.

As shown in FIG. 6A, the barrier layers 47, 48 are disposed on theopposite sides of the quantum dot layer 46, respectively. An adhesivelayer may be included between the quantum dot layer 46 and each of thebarrier layers 47, 48, and in this Embodiment, it is possible to formthe barrier layers 47, 48 brought into contact with the both surfaces ofthe quantum dot layer 46. By thus providing the barrier layers 47, 48,the both surfaces of the quantum dot layer 46 are protected, and it ispossible to improve environmental resistance (durability).

Each of the barrier layers 47, 48 is formed of a single layer of anorganic layer, or laminate structure of an organic layer and inorganiclayer. As the organic layer, it is possible to exemplify a PET(polyethylene terephthalate) film. Further, as the inorganic layer, itis possible to exemplify a SiO₂ layer. Alternatively, the inorganiclayer may be a layer of silicon nitride (SiN_(x)), aluminium oxide(Al₂O₃) , titanium oxide (TiO₂), or silicon oxide (SiO₂), or a laminatethereof.

The sheet member 45 including quantum dots is capable of beingincorporated into a backlight apparatus 73 shown in FIG. 6B, forexample. In FIG. 6B, the backlight apparatus 73 is comprised by having aplurality of light emitting devices 72 (LEDs) and the sheet member 45opposed to the light emitting devices 72. As shown in FIG. 6B, each ofthe light emitting devices 72 is supported on the surface of a supportbody 71. In FIG. 6B, the backlight apparatus 73 is disposed on the backside of a display section 74 such as a liquid crystal display, therebyconstituting a display apparatus 70.

In addition, although not shown in FIG. 6B, as well as the sheet member45, a diffusion plate that diffuses light, another sheet and the likemay exist between the light emitting devices 72 and the display section74.

Further, the sheet member 45 is formed of a single sheet, and forexample, a plurality of sheet members 45 may be joined to be apredetermined size. Hereinafter, the configuration where a plurality ofsheet members 45 is joined by tiling is referred to as a composite sheetmember.

In FIG. 6C, components are disposed in the order of light emittingdevices 72/composite sheet member 75/diffusion plate 76/display section74. By this means, even when unevenness of an emitted color caused bydiffuse reflection, deterioration of quantum dots by water vaporentering from a joint or the like occurs in the joint of sheet membersconstituting the composite sheet member 75, it is possible to suitablysuppress that color unevenness occurs in display of the display section74. In other words, the light released from the composite sheet member75 is diffused by the diffusion plate 76, and then, is input to thedisplay section 74, and it is thereby possible to suppress colorunevenness in display in the display section 74.

FIG. 7A is a perspective diagram of a wavelength conversion memberprovided with quantum dots and FIG. 7B is a cross-sectional diagramalong arrows A-A. FIG. 7A is the perspective diagram of the wavelengthconversion member, and FIG. 7B is the cross-sectional diagram of thewavelength conversion member shown in FIG. 7A taken along line A-A inthe plane direction, viewed from the arrow direction.

As shown in FIG. 7A, the wavelength conversion member 50 has a container51, and a compact 52 including a wavelength conversion substance to becomprised thereof.

The container 51 is provided with storage space 53 capable of storingthe compact 52 including the wavelength conversion substance to hold. Itis preferable that the container 51 is a transparent member.“Transparent” refers to a member generally regarded as beingtransparent, or a member in which visible light transmittance is about50% or more.

Horizontal and vertical dimensions of the container 51 range from aboutseveral millimeters to several tens of millimeters, and horizontal andvertical dimensions of the storage space 53 range from about severalhundreds of micrometers to several millimeters.

As shown in FIGS. 7A and 7B, the container 51 is provided with a lightinput surface 51 a, light output surface 51 b, and side surfaces 51 cconnecting between the light input surface 51 a and the light outputsurface 51 b. As shown in FIGS. 7A and 7B, the light input surface 51 aand the light output surface 51 b are in a position relationship wherethe surfaces are opposed to each other.

As shown in FIGS. 7A and 7B, in the container 51, the storage space 53is formed on the inner side of the light input surface 51 a, the lightoutput surface 51 b and the side surface 51 c. In addition, a part ofthe storage space 53 may reach the light input surface 51 a, the lightoutput surface 51 b or the side surface 51 c.

The container 51 shown in FIGS. 7A and 7B is a container formed of aglass tube, for example, and it is possible to exemplify a glasscapillary. In addition, as long as it is possible to form a containerwith excellent transparency as described above, the container may bemade of a resin or the like.

As shown in FIGS. 7A and 7B, in the storage space 53 is disposed thecompact 52 including the wavelength conversion substance. As shown inFIGS. 7A and 7B, the storage space 53 is open, and it is possible toinsert the compact 52 including the wavelength conversion substancetherefrom.

It is possible to insert the compact 52 including the wavelengthconversion substance into the storage space 53 by means such asinjection and adhesion. In the case of injection, the compact 52including the wavelength conversion substance is formed in thecompletely same size as that of the storage space 53, or is formed to beslightly larger than the storage space 53, and by inserting the compact52 including the wavelength conversion substance into the storage space53, while applying pressure, it is possible to suppress the fact thatgaps occur not only inside the compact 52 including the wavelengthconversion substance, but also between the compact 52 including thewavelength conversion substance and the container 51.

Further, in the case of bonding the compact 52 including the wavelengthconversion substance to the inside of the storage space 53 to fix, thecompact 52 including the wavelength conversion substance is formed to besmaller than the storage space 53, and in a state in which an adhesivelayer is applied to the side surfaces of the compact 52 including thewavelength conversion substance, is inserted into the storage space 53.At this point, the cross-sectional area of the compact 52 may beslightly smaller than the cross-sectional area of the storage space 53.By this means, the compact 52 including the wavelength conversionsubstance and the container 51 are brought into intimate contact witheach other via the adhesive layer, and it is possible to suppress thefact that gaps are formed between the compact 52 including thewavelength conversion substance and the container 51. As the adhesivelayer, it is possible to use the same resin as the compact 52, or aresin that the basic structure is common to the compact 52. Further, asthe adhesive layer, a transparent adhesive may be used.

Furthermore, it is preferable that a refractive index of the compact 52including the wavelength conversion substance is smaller than arefractive index of the container 51. By this means, a part of the lightentering into the compact 52 including the wavelength conversionsubstance is totally reflected by side wall portions of the container 51facing the storage space 53. This is because an incident angle on themedium side with a low refractive index is larger than an incident angleon the medium side with a high refractive index. By this means, it ispossible to decrease an amount of light leaking from the side to theoutside of the container 51, and it is thereby possible to enhance colorconversion efficiency and light emission intensity.

A light emitting device is disposed on the light input surface 51 a sideof the wavelength conversion member 50 shown in FIGS. 7A and 7B.Further, the light guide plate 40 shown in FIG. 4 and the like aredisposed on the light output surface 51 b side of the wavelengthconversion member 50. In addition, FIGS. 7A and 7B illustrates thecompact 52, and a quantum dot layer may be formed by injecting a resincomposition including quantum dots.

FIG. 8 is a perspective diagram of a light emitting device having awavelength conversion member provided with quantum dots to be comprisedthereof. FIG. 9 is a longitudinal sectional diagram taken along line B-Bin the height direction viewed from the arrow direction in a state inwhich each component of the light emitting device shown in FIG. 8 iscombined.

The light emitting device 55 shown in FIGS. 8 and 9 has a wavelengthconversion member 56 and LED chip (light emitting section) 65 to becomprised thereof. The wavelength conversion member 56 is provided witha container 59 comprised of a plurality of pieces including a containermain body 57 and a lid body 58. Further, as shown in FIG. 8, in thecenter portion of the container main body 57 is formed storage space 60with the bottom. In the storage space 60 is provided a wavelengthconversion layer 64 including quantum dots. The wavelength conversionlayer 64 may be a compact, or may be filled inside the storage space 60by potting processing and the like. Then, the container main body 57 andlid body 58 are joined via an adhesive layer.

A light input surface 59 a is a lower surface of the container 59 of thewavelength conversion member 56 shown in FIGS. 8 and 9. A light outputsurface 59 b is an upper surface opposite the light input surface 59 a.The storage space 60 is formed in a position on the inner side withrespect to each side surface 59 c provided in the container 59 of thewavelength conversion member 56 shown in FIGS. 8 and 9.

As shown in FIG. 9, the LED chip 65 is connected to a printed wiringboard 61, and as shown in FIGS. 8 and 9, the circumference of the LEDchip 65 is enclosed with a frame body 62. Then, the inside of the framebody 62 is sealed with a resin layer 63.

As shown in FIG. 9, the wavelength conversion member 56 is joined to theupper surface of the frame body 62 via an adhesive layer not shown, andthe light emitting device 55 such as an LED is thereby comprised.

The quantum dot of this Embodiment has the following features. In otherwords, in the quantum dot of Embodiment 1, in a TG-DTA(Thermogravimetry•Differential Thermal Analysis) profile, a weightreduction up to 490° C. is within 75%. In this way, in Embodiment 1,organic residues adhering to the surface of the quantum dot areevaluated by the weight reduction (TG). As shown in experimentsdescribed later, it has been understood that the weight reduction of aquantum dot of Comparative Example is about 90% or more up to 490° C. Inother words, organic residues with a weight about nine times the quantumdot itself adhere to the surface of the quantum dot of the ComparativeExample. In contrast thereto, in the quantum dot in Embodiment 1, theweight reduction up to 490° C. is within 75%, and organic residuesadhering to the surface of the quantum dot are fewer than those of theComparative Example.

Embodiment 2 provides a quantum dot that oleylamine (OLA) is notobserved in GC-MS qualitative analysis at 350° C. Thus, in Embodiment 2,organic residues adhering to the surface of the quantum dot areevaluated by qualitative analysis at 350° C., and herein, 350° C. is atemperature at which an abrupt weight change started to occur in TG-DTA.Further, in the quantum dot of Embodiment 2, it is preferable thattrioctylphosphine (TOP) is not observed in GC-MS qualitative analysis at350° C. On the other hand, as shown in experiments described later,oleylamine (OLA) and trioctylphosphine (TOP) were observed in GC-MSqualitative analysis of the quantum dot of the Comparative Example.

For the quantum dot, at least one of the above-mentioned TG-DTA andGC-MS qualitative analysis is performed, and it is essential only thatthe weight reduction up to 490° C. is within 75% in a TG-DTA profile, orthat oleylamine (OLA) is not observed in GC-MS qualitative analysis at350° C. In other words, when the condition of the above-mentionedEmbodiment 1 is satisfied, satisfaction of the condition of Embodiment 2is not a requirement. Similarly, when the condition of theabove-mentioned Embodiment 2 is satisfied, satisfaction of the conditionof Embodiment 1 is not a requirement. In addition, in the case whereboth of the above-mentioned TG-DTA and GC-MS qualitative analysis areperformed on a quantum dot, the weight reduction up to 490° C. is within75% in a TG-DTA profile, and oleylamine (OLA) is not observed in GC-MSqualitative analysis at 350° C., it is possible to decrease organicresidues adhering to the surface of the quantum dot more reliably, andsuch a case is suitable.

In this Embodiment, by configuring a fluorescent layer of a lightemitting apparatus using quantum dots with few organic residues adheringto the surface, it is possible to effectively suppress the occurrence ofblack discoloration inside the fluorescent layer positioned immediatelyabove the light emitting device, and to enhance luminous efficiency.

For example, the quantum dot of the present invention is manufactured bysteps as shown in FIG. 10. FIG. 10 is a flowchart illustrating a methodof manufacturing the quantum dot.

In step ST1 shown in FIG. 10, the core portion 7 is synthesized. Forexample, formed is the core portion 7 made of ZnCdSeS synthesized byreacting raw materials obtained by preparing an Se source, Cd source, Znsource, S source and the like by a micro-reactor method.

Next, in step ST2 shown in FIG. 10, the surface of the core portion 7 iscoated with the first shell portion 9. For example, the surface of thecore portion 7 is coated with the first shell portion 9 made of ZnCdSsynthesized by reacting raw materials obtained by preparing an S source,Cd source, Zn source and the like by a continuous injection method.

Next, in step ST3 shown in FIG. 10, the surface of the first shellportion 9 is coated with the second shell portion 10. For example, thesurface of the first shell portion 9 is coated with the second shellportion 10 made of ZnS synthesized by reacting ZnS materials by thecontinuous injection method.

For example, as the Zn source, used as an example are zinc oxide, oleicacid, 1-octadecene and oleylamine (OLA). As a substitute for zinc oxide,it is possible to use [(CH₃)₂NCSS]₂Zn, [(C₂H₅)₂NCSS]₂Zn,C₂H₅ZnS₂CN(C₂H₅)₂, Cd[S₂CNCH₃(C₆H₅)]₂ and the like. Alternatively, inthe case of coating of ZnSe, it is possible to use Zn[Se₂CNCH₃(C₆H₅)]₂and the like. In the case of forming one of the shell portions 9 and 10,one of steps ST2 and ST3 is selected. Further, in the case where theshell portions 9 and 10 are not formed, steps ST2 and ST3 are notselected.

Next, in step ST4 shown in FIG. 10, a quantum dot solution obtained asdescribed above is cleaned. In a cleaning step, an undiluted solution ofquantum dots is mixed into solvents such as toluene and ethanol, and thequantum dots and solvents are subjected to centrifugation with acentrifuge. Then, the solvents are discharged to obtain the cleanedquantum dots.

FIG. 11 is a schematic diagram illustrating a first method of cleaningthe quantum dot in the present invention. In the first cleaning methodshown in FIG. 11, used is a centrifuge capable of applying a centrifugalforce of about several thousands of G.

First, in the first cleaning, a solvent 22 is poured in a container 21including an undiluted solution (referred to as “QD undiluted solution”)of quantum dots generated through steps ST1 to ST3 shown in FIG. 10. Thesolvent 22 is alcohols, ketone, toluene and the like.

Next, the mixed solution of the QD undiluted solution and solvent 22 isapplied to the first-time centrifuge. At this point, for example, thecentrifugal force of 8,000 rpm is caused to act for 10 minutes. By thismeans, it is possible to properly separate the quantum dot 23 and thesolvent 24 by centrifugation. Then, the solvent 24 is discharged.

Next, the second cleaning is performed. First, a solvent 25 is mixedinto the quantum dot cleaned as described above, and at this point, itis possible to make an amount of the solvent 25 to pour smaller than anamount of the solvent 22 poured in the first cleaning. Then, theresultant is subjected to the second-time centrifuge. For example, thecentrifugal force of 8,000 rpm is caused to act for 5 minutes. By thismeans, it is possible to properly separate the quantum dot 26 and thesolvent 27 by centrifugation. Then, the solvent 27 is discharged.

The quantum dot thus obtained through a plurality of cleanings isrecovered to obtain a quantum dot concentrated solution (referred to asQD concentrated solution) 28 dispersed in ODE, for example.

FIG. 12 is a schematic diagram illustrating a second method of cleaningthe quantum dot. In the second cleaning method shown in FIG. 12, used isan ultracentrifuge capable of applying a centrifugal force of severaltens of thousands of G or more.

In FIG. 12, a QD undiluted solution 30 is applied to theultracentrifuge. At this time, for example, the centrifugal force of230,000 xg is caused to act for 15 minutes. By this means, it ispossible to separate the quantum dot 31 and the solvent 32 bycentrifugation. Then, the solvent 32 is discharged. The quantum dotobtained through cleaning by the ultracentrifuge is recovered to obtaina QD concentrated solution. The ultracentrifuge is used in cleaning inFIG. 12, and as the number of revolutions, 40,000 rpm or more ispreferable.

In this Embodiment, by applying the cleaning step using a centrifuge(preferably ultracentrifuge) to the quantum dot, it is possible toeffectively remove unnecessary organic residues adhering (adsorbed) tothe surface of the quantum dot.

Further, in the above-mentioned description, the cleaning step isapplied, after the synthesis of the core portion (step ST1), formationof the first shell portion (step ST2) and formation of the second shellportion (step ST3), and it is also possible to perform cleaning for eachstep.

In other words, after the synthesis of the core portion, solvents suchas toluene and ethanol are poured into a container with an undilutedsolution of the core portion put therein, and the resultant is stirred,shaken and mixed. Then, centrifugation is performed to precipitate andrecover the core portion. Subsequently, a supernatant solution isremoved, and after drying, for example, octadecene (ODE) is added toperform re-dispersion. When re-dispersion is hard to perform, ultrasonicis applied.

Successively, after the formation of the first shell portion, a solventsuch as toluene is poured into a container with an undiluted solution ofthe quantum dot put therein, and the resultant is stirred, shaken andmixed. Subsequently, a solid of a by-product and the like isprecipitated from the mixed solution, and for example, the quantum dotis extracted to toluene. Then, supernatant toluene including the quantumdot is recovered, and is concentrated using an evaporator. Again, asolvent such as ethanol is poured, the resultant is stirred, shaken andmixed, and after discarding a supernatant solution, centrifugation isperformed to precipitate and recover the quantum dot. Successively, asupernatant solution is removed, and after drying, for example,octadecene (ODE) is added to perform re-dispersion. When re-dispersionis hard to perform, ultrasonic is applied.

Next, after the formation of the second shell portion, the resultant isconcentrated using the evaporator. Successively, a solvent such astoluene is poured, stirred and shaken, a solvent such as ethanol ispoured, stirred and shaken, and a supernatant solution is removed. Then,centrifugation is performed to precipitate and recover the quantum dot.Successively, a supernatant solution is removed, and after drying, forexample, toluene is added to perform re-dispersion. When re-dispersionis hard to perform, ultrasonic is applied. In addition, when the amountis large and centrifugation is hard to apply, spontaneous precipitationmay be performed.

According to the quantum dot obtained by the above-mentionedmanufacturing method, it is possible to make the weight reduction from50° C. to 490° C. within 75% in a TG-DTA ((Thermogravimetry•DifferentialThermal Analysis) profile. Further, as described above, the Zn source ingenerating the quantum dot of the present invention includes oleylamine(OLA), but according to the dot obtained by the above-mentionedmanufacturing method, the oleylamine (OLA) is not observed in GC-MSqualitative analysis at 350° C. Accordingly, by the cleaning step usingthe centrifuge, it is possible to effectively remove organic residuesincluding the oleylamine (OLA) adhering to the surface of the quantumdot 5.

By dispersing the quantum dot 5 that organic residues on the surface aresuitably removed, for example, in the fluorescent layer 4 shown in FIG.1A or 1B, when the LED chip 3 emits light, it is possible to effectivelysuppress the black discoloration occurrence inside the fluorescent layer4 positioned immediately above the LED chip 3, and to improve luminousefficiency. Accordingly, according to this Embodiment, it is possible toobtain the light emitting apparatus without black discolorationoccurring. The black discoloration occurs in the fluorescent layer 4including the quantum dot 5 positioned immediately above the LED chip 3,and as the reason why the black discoloration occurs, the cause isconsidered the effect of light, heat or both from the LED chip 3 on thequantum dot including a large amount of organic residues in theconventional technique.

Further, by dispersing the quantum dot 5 that organic residues on thesurface are suitably removed in the fluorescent layer 29 shown in FIG.3, the wavelength conversion member 42 shown in FIG. 4, the wavelengthconversion sheet 43 shown in FIG. 5, the quantum dot layer 46 shown inFIG. 6A, the compact 52 shown in FIGS. 7A and 7B and the wavelengthconversion layer 64 shown in FIG. 8, as in the case of FIG. 1A or 1B, itis possible to enhance the effect of suppressing the black discolorationoccurrence and to suitably improve luminous efficiency.

Herein, the fact that “black discoloration does not occur” in thepresent Description refers to the fact that deterioration of lightemission intensity at an emission wavelength indicative of a peak in anemission spectrum of a light emitting apparatus is suppressed within 30%after a lighting test of the light emitting apparatus, as compared withbefore the test. As the lighting test, for example, light emissionintensity is measured after performing lighting at 85° C. for 1000hours, and it is possible to compare with intensity when blackdiscoloration does not occur immediately before the durability test. Inother words, after performing the lighting test of the light emittingapparatus at 85° C. for 1000 hours, when deterioration of light emissionintensity at an emission wavelength indicative of a peak in an emissionspectrum of the light emitting apparatus is suppressed within 30% ascompared with before the test, it is recognized that black discolorationdoes not occur. As an example, in the LED apparatus 38 using the LEDchip 3 that emits blue light, the quantum dot 5 that emits green light,and the quantum dot 5 that emits red light, when the light emission testis performed at 85° C. for 1000 hours, in the case where it is possibleto suppress deterioration of light emission intensity at a peakwavelength of each of RGB after the test is all suppressed within 30% ascompared with the light emission intensity at each of the samewavelengths before the test, the case is referred to as that the blackdiscoloration does not occur.

As described above, as the cleaning step, the quantum dot and solventare separated by centrifugation using the centrifuge or ultracentrifuge,and by the centrifugation, it is possible to effectively remove organicresidues such as oleylamine (OLA) adhering to the surface of the quantumdot.

In the case of using the centrifuge described in FIG. 11, as the numberof revolutions, it is preferable that the number is 7000 rpm or more(the centrifugal force is about 8300 xg at 7000 rpm in H-9R made byKOKUSAN Co., Ltd.) Further, the time required for centrifugation ispreferably 5 minutes or more. Furthermore, the number of times ofcentrifugation is preferably two or more.

Further, in the case of using the ultracentrifuge, it is preferable thatthe number of revolution is 40,000 rpm or more (230,000 xg or more), andthat the time required for centrifugation is 15 minutes or more. In thecase of using the ultracentrifuge, the number of times of centrifugationis preferably one or more. In the case of using the ultracentrifuge, itis possible to decrease the total solvent amount and total cleaningtime, and to result in reduction in manufacturing cost. Furthermore, itis possible to more effectively promote concentration precipitation ofquantum dots, and it is expected to enhance the cleaning effect by theconcentration precipitation. Still furthermore, it is possible toeliminate alien particle dots such that the particle diameter isextremely small and the like, it is possible to expect improvements inquantum yield (QY).

Example

The present invention will specifically be described below, usingExamples performed to clarify the effects of the invention andComparative Examples. In addition, the invention is not limited by thefollowing Examples at all.

The core portion of the quantum dot used in experiments was formed ofCdS, CdSe, ZnS, ZnSe or combination thereof using a micro-reactormethod. The synthesis temperature was set at about 320° C., the flowrate of solution sending was set at about 320 μL/min, and the reactiontime was set at 120 sec. In addition, the inner diameter(diameter)×length of the reaction section (capillary) was 320 μm×8 m.

Successively, the surface of the core portion was coated with the firstshell portion using ZnCdS. Specifically, ZnCdS was formed by synthesisusing raw materials obtained by preparing ODE, S source, Cd source, andZn source by a continuous injection method. The set temperature wasabout 360° C., the flow rate of solution sending was set at about 400μL/min (first stage), and about 800 μL/min (second stage), the solutionsending amount of raw materials was set at about 5 mL (first time), andabout 20 mL (second time), and the reaction time was set at about 13minutes (first stage) , about 250 minutes (second stage), and 5 minutes(annealing).

Successively, the surface of the first shell portion is coated with thesecond shell portion using ZnS. Specifically, ZnS was formed bysynthesis using raw materials obtained by preparing TOP and ZnS rawmaterials by the continuous injection method. The set temperature wasabout 290° C., the flow rate of solution sending was set at about 800μL/min, the solution sending amount was set at about 20 mL, and thereaction time was set at about 20 minutes.

Example

Cleaning shown in FIG. 11 was performed on quantum dots (green) with theabove-mentioned core/multi-shell structure.

(Centrifuge)

Apparatus Name: H-9R made by KOKUSAN Co., Ltd.Condition: 9500 xg (8000 rpm)Time: 10 minutes (first cleaning), 5 minutes (second cleaning)

The QD undiluted solution in the first cleaning was 50 mL, and as thesolvent, 36 mL of toluene and 240 mL of ethanol were used. Further, inthe second cleaning, as the solvent, 150 mL and 8 mL of ethanol wasused. Then, quantum dots obtained via the cleaning step were dispersedin ODE to obtain a QD concentrated solution.

Comparative Example 1

As in the Example, cleaning using the centrifuge (H-9R made by KOKUSANCo., Ltd.) was performed twice. In addition, the condition of thecentrifuge and solvents were changed. In other words, in the firstcleaning, the QD undiluted solution was 0.5 mL, and as the solvent, 9 mLof ethanol was used. Further, the condition of the centrifuge used inthe first cleaning was set at 5400 xg (5500 rpm), and the centrifugationtime was set at 5 minutes. Furthermore, in the second cleaning, 9 mL ofethanol was used as the solvent, the condition of the centrifuge used inthe second cleaning was set at 5400 xg (5500 rpm), and thecentrifugation time was set at 5 minutes. Then, quantum dots obtainedvia the cleaning step were dispersed in 0.5 mL of toluene to obtain a QDconcentrated solution.

Comparative Example 2

Except that toluene used in the first cleaning in Example 1 was replacedwith a solvent of dodecanthiol (DDT) (40%) and toluene (60%), thecleaning was performed as in Comparative Example 1.

In the Example, the dispersion state of quantum dots was excellent,there was no turbidity, and suspended matter•precipitate was notobserved.

On the other hand, in Comparative Examples 1 and 2, the dispersion stateof quantum dots was poor as compared with the Example, and further,turbidity and suspended matter•precipitate was observed.

Next, with respect to quantum dots respectively obtained via thecleaning steps of the above-mentioned Example and Comparative Examples 1and 2, an organic substance amount remaining on the quantum dot surfacewas evaluated with a weight reduction (TG) by TG-DTA(Thermogravimetry•Differential Thermal Analysis) measurement.

(TG-DTA)

Apparatus name: TGDTA 6300 made by SII•Technology

Kabushiki Kaisha Atmosphere: In the air

Measurement temperature range: From 50° C. to 550° C.Rate of temperature rise: 10° C./min

FIG. 13 is a TG-DTA profile of the quantum dot in the Example, FIG. 14is a TG-DTA profile of the quantum dot in Comparative Example 1, andFIG. 15 is a TG-DTA profile of the quantum dot in Comparative Example 2.

The weight reduction (TG) is discussed. In any of samples of FIG. 13 toFIG. 15, when the temperature was raised to about 350° C., gentle weightreductions were observed in the same manner. In the TG-DTA profile ofthe quantum dot in the Example shown in FIG. 13, when the temperaturewas raised from 50° C. to about 350° C., the weight reduction of 3% wasobserved. In the TG-DTA profile of the quantum dot in ComparativeExample 1 shown in FIG. 14, when the temperature was raised from 50° C.to about 350° C., the weight reduction of 2% was observed. T_(n) theTG-DTA profile of the quantum dot in Comparative Example 2 shown in FIG.15, when the temperature was raised from 50° C. to about 350° C., theweight reduction of 4% was observed.

On the other hand, when the temperature exceeded around 350° C., abruptweight reductions were observed in any of the samples, and were almostconstant at around 490° C.

However, in the Example and Comparative Examples, the followingdifference was observed. In the Example, as shown in FIG. 13, in theTG-DTA profile, the weight reduction (TG) from 50° C. to 490° C. waswithin 75%, and specifically, was 72%. In other words, in the Example,the weight reduction in raising the temperature from 350° C. to 490° C.was within 70%, and specifically, was 69%. In contrast thereto, it wasfound that in Comparative Example 1 shown in FIG. 14, the weightreduction (TG) from 50° C. to 490° C. was about 93%, and that inComparative Example 2 shown in FIG. 15, the weight reduction (TG) from50° C. to 490° C. was about 90%. In other words, in Comparative Example1, the weight reduction in raising the temperature from 350° C. to 490°C. was about 91%. In Comparative Example 2, the weight reduction inraising the temperature from 350° C. to 490° C. was about 86%. In otherwords, in the Comparative Examples, it was understood that organicresidues with a weight about nine times the quantum dot itself existedon the surface of the quantum dot. In contrast thereto, in the Example,it is possible to suppress organic residues adhering to the surface ofthe quantum dot within a weight about seven times the quantum dot orless.

Thus, in the quantum dot of the Example, it was understood that organicresidues adhering to the surface are a few as compared with the quantumdots of the Comparative Examples.

Next, with respect to quantum dots respectively obtained via thecleaning steps of the above-mentioned Example and Comparative Example 1,qualitative analysis was performed at 350° C. at which the abrupt weightreduction started in TG-DTA measurement.

(GC-MS)

Apparatus name: GC-2010 (GC part), GCMS-QP 2010 (MS part) made byShimadzu CorporationColumn: Ultra Alloy 5 made by Frontier Lob., Length 30 m, Film thickness0.25 μm, Inner diameter 0.25 mm ID Electron ionization energy: 70 eVRate of temperature rise: 50° C./min from 35° C. to 320° C.,subsequently 320° C. was kept for 12 minutes and 30 seconds.

Carrier gas: Helium

As a procedure of qualitative analysis, a GC spectrum at 350° C. ismeasured, and each peak of the spectrum is selected to analyze an MSspectrum. Then, candidate substances with high matching degrees (SI) areautomatically extracted from the database (DB), and identification isperformed by comparing the MS spectrum, the MS spectrum of the candidatesubstance of the DB and the matching degree. At this point, when SI is90% or more, it is possible to obtain high reliability. Theabove-mentioned procedure is performed on each GC spectrum.

FIG. 16 is a GC-MS spectrum (350° C.) of the quantum dot in the Example,and FIG. 17 is a GC-MS spectrum (350° C.) of the quantum dot incomparative Example 1.

Based on the above-mentioned qualitative analysis, as shown in FIG. 16,in the Example, octadecene (ODE) and trioctylphosphine oxide (TOPO) wereobserved. On the other hand, in Comparative Example 1 shown in FIG. 17,as well as ODE and TOPO, oleylamine (OLA) and trioctylphosphine (TOP)were observed. In addition, TOPO is an oxide of TOP.

In the Example with excellent dispersion characteristics, as shown inFIG. 16, the intensity of the GC spectrum is weak, and it is possible topresume that organic residues adhering to the quantum dot surface are afew. Actually, observed spectra were only the ODE spectrum and TOPOspectrum.

On the other hand, in the Comparative Example with poor dispersioncharacteristics, as shown in FIG. 17, ODE, OLA, TOP and TOPO wereobserved which were organic residues having sharp peaks. As the reasonwhy OLA and TOP that were not observed in the Example were observed inthe Comparative Example, it is considered that organic substancesderived from raw materials used in the generation process of the quantumdot were suitably not removed in the cleaning step.

(Black Discoloration Examination of the LED Apparatus)

When the LED apparatus shown in FIG. 1A was prepared using the quantumdot of the Comparative Example in the fluorescent layer, blackdiscoloration was observed inside the fluorescent layer 4 positionedimmediately above the LED chip 3. In FIG. 1A, black discoloration wasobserved inside the fluorescent layer 4 in a portion in contact with theupper surface of the LED chip 3. In the configuration shown in FIG. 1B,black discoloration was observed inside the fluorescent layer 4 in thevicinity of the boundary between the fluorescent layer 4 and the resinlayer 12 above the LED chip 3.

On the other hand, when the LED apparatuses shown in FIGS. 1A and 1Bwere prepared using the quantum dot of the Example in the fluorescentlayer, as distinct from the Comparative Example, black discoloration wasnot seen in the fluorescent layer 4 positioned immediately above the LEDchip 3. In other words, when the LED apparatus is prepared using thequantum dot of the Example in the fluorescent layer and the lightemission test is performed at 85° C. for 1000 hours, deterioration oflight emission intensity at a peak wavelength of each of RGB after thetest is all suppressed within 30% as compared with the light emissionintensity at each of the peak wavelengths of RGB before the test. Bythis means, it is possible to obtain the LED apparatus without blackdiscoloration occurring.

As described above, the conditions of the cleaning step were differentbetween the quantum dot of the Example and the quantum dot of theComparative Example, and in the Example, from the results of the TG-DTAprofile and GM-MS analysis, it was understood that it is possible toreduce organic residues adhering to the quantum dot surface, as comparedwith the Comparative Example. By this means, in the Example, it isconsidered that a large amount of organic residues were not taken in thefluorescent layer of the LED apparatus as compared with the Comparativeexample, thereby resulting in reduction in black discoloration. Inaddition, the experiments were performed in the LED apparatuses of FIG.1A or 1B, and in each of configurations as shown in FIGS. 4 to 9, it ispossible to similarly suppress the black discoloration occurrence.

(In Regard to Cleaning with the Centrifuge)

For example, the condition of the centrifuge in the Example was set at8,875 xg, and the centrifugation time was set at 5 minutes (first time),and at 2 minutes (second time). Further, with respect to 50 mL of the QDundiluted solution, the solvent used in the first time was made of 43.4g (50 mL) of toluene, and 63.2 g (80 mL) of ethanol. Further, thesolvent used in the second-time cleaning was made of 2.3 g (2.7 mL) oftoluene, and 6.3 g (8 mL) of ethanol. Then, the recovered QD wasdispersed in 2 mL of toluene to obtain a QD concentrated solution. Ascompared with the conditions of the Example as shown in FIG. 11, it wascontrolled that the rotation of the centrifuge was fast, and that thecentrifugation time was short. Further, it was possible to also decreasethe amount of the solvent. When the TG-DTA profile of the quantum dotwas measured on the same conditions as in the Example, the weightreduction (TG) from 50° C. to 490° C. was within 75%. Furthermore, theweight reduction in raising the temperature from 350° C. to 490° C. waswithin 70%. Still furthermore, when the GC-MS spectrum of the quantumdot at 350° C. was measured on the same condition as in the Example,octadecene (ODE) and trioctylphosphine oxide (TOPO) were observed, andoleylamine (OLA) and trioctylphosphine (TOP) were not observed. When theLED apparatuses shown in FIGS. 1A and 1B were prepared using the quantumdot in the fluorescent layer, black discoloration was not seen in thefluorescent layer 4 positioned immediately above the LED chip 3. Inother words, when the LED apparatus is prepared using the quantum dot ofthe Example in the fluorescent layer and the light emission test isperformed at 85° C. for 1000 hours, deterioration of light emissionintensity at a peak wavelength of each of RGB after the test is allsuppressed within 30% as compared with the light emission intensity ateach of the peak wavelengths of RGB before the test. By this -means, itis possible to obtain the LED apparatus without black discolorationoccurring.

(In Regard to Cleaning with the Ultracentrifuge)

A concentration test of the quantum dot was performed using thefollowing ultracentrifuge.

Apparatus name: BecKman Optima MAX-XPCondition: 435,000 xg (100,000 rpm)Time: 15 minutes

Using quantum dots of two kinds of core/multi-shell structures ofZnCdSeS (Green)/ZnCdS (Shell I)/ZnS (Shell II) and CdSe (Red)/ZnCdS(Shell I)/ZnS (Shell II), QD concentrated solutions were obtained basedon the steps shown in FIG. 12. In any of the solutions, concentrationprecipitation of quantum dots was seen.

According to the cleaning step using the ultracentrifuge, as comparedwith the cleaning step using the centrifuge, it is possible toeffectively promote concentration precipitation, and it is expected toenhance the cleaning effect by the concentration precipitation. Further,it is possible to decrease the solvent amount and cleaning time, and itis possible to reduce the manufacturing cost. When the TG-DTA profile ofthe quantum dot was measured on the same condition as in the Example,the weight reduction (TG) from 50° C. to 490° C. was within 75%.Furthermore, the weight reduction in raising the temperature from 350°C. to 490° C. was within 70%. Still furthermore, when the GC-MS spectrumof the quantum dot at 350° C. was measured on the same condition as inthe Example, octadecene (ODE) and trioctylphosphine oxide (TOPO) wereobserved, and oleylamine (OLA) and trioctylphosphine (TOP) were notobserved. When the LED apparatuses shown in FIGS. 1A and 1B wereprepared using the quantum dot in the fluorescent layer, blackdiscoloration was not seen in the fluorescent layer 4 positionedimmediately above the LED chip 3. In other words, when the LED apparatusis prepared using the quantum dot of the Example in the fluorescentlayer and the light emission test is performed at 85° C. for 1000 hours,deterioration of light emission intensity at a peak wavelength of eachof RGB after the test is all suppressed within 30% as compared with thelight emission intensity at each of the peak wavelengths of RGB beforethe test. By this means, it is possible to obtain the LED apparatuswithout black discoloration occurring.

INDUSTRIAL APPLICABILITY

By dispersing the quantum dot of the present invention in thefluorescent layer of the LED apparatus, it is possible to manufacturethe LED apparatus without black discoloration occurring in thefluorescent layer positioned immediately above the LED chip. As thelight emitting device, as well as an LED, it is possible to adoptorganic EL and the like. By varying materials of the quantum dot used inthe fluorescent layer, it is possible to convert a wavelength of colorin the florescent layer into various wavelengths, and it is possible tomanufacture the light emitting apparatus which has a wide variety offluorescent colors without black discoloration occurring and has longapparatus life.

The present application is based on Japanese Patent Application No.2014-079562 filed on Apr. 8, 2014, entire content of which is expresslyincorporated by reference herein.

1. A quantum dot, wherein a weight reduction up to 490° C. is within 75%in a TG-DTA profile.
 2. A quantum dot, wherein oleylamine (OLA) is notobserved in GC-MS qualitative analysis at 350° C.
 3. The quantum dotaccording to claim 2, wherein trioctylphosphine (TOP) is not observed inGC-MS qualitative analysis at 350° C.
 4. The quantum dot according toclaim 2, wherein a weight reduction up to 490° C. is within 75% in aTG-DTA profile.
 5. A quantum dot, wherein the dot is cleaned with anultracentrifuge.
 6. The quantum dot according to claim 1, wherein thequantum dot is comprised of a core portion including a semiconductorparticle, and a shell portion coating the surface of the core portion.7. The quantum dot according to claim 6, wherein the shell portion has afirst shell portion coating the core portion, and a second shell portioncoating the surface of the first shell portion is coated.
 8. A compactcomprising the quantum dot according to claim
 1. 9. A sheet membercomprising the quantum dot according to claim
 1. 10. A wavelengthconversion member comprising: a container provided with storage space;and a wavelength conversion layer including the quantum dot according toclaim 1, the wavelength conversion layer disposed inside the storagespace.
 11. A light emitting apparatus having a fluorescent layercovering a light emitting side of a light emitting device, wherein thefluorescent layer is formed of a resin with the quantum dot according toclaim 1 dispersed.
 12. A light emitting apparatus having a fluorescentlayer covering a light emitting side of a light emitting device, whereinthe fluorescent layer is formed of a resin with quantum dots dispersed,and black discoloration by emission of the light emitting device doesnot occur in the resin layer.
 13. A method of manufacturing a quantumdot having a core portion including a semiconductor particle, wherein aquantum dot solution is prepared by including a step of synthesizing thesemiconductor particle to form the core portion, and an ultracentrifugeis used in a step of cleaning the quantum dot solution.
 14. The methodof manufacturing a quantum dot according to claim 13, wherein the methodincludes a step of coating the surface of the core portion with a shellportion after the step of forming the core portion, and shifts to thecleaning step after coating the surface of the core portion with theshell portion.
 15. The method of manufacturing a quantum dot accordingto claim 14, wherein the shell portion is formed of a first shellportion coating the core portion, and a second shell portion coating thesurface of the first shell portion.